A. Field of the Invention
This invention relates to telephones having provision for the installation of auxiliary processing devices.
B. Related Art
Feature telephones commonly have a face which includes a number of keys and a number of visual indicators, such as light emitting diodes (LEDs). For example, as illustrated in FIG. 10, a base telephone 1002 can include a number of keys 1004 each having an adjacently located LED 1006. Commonly, the telephone 1002 will be connected to a private branch exchange (PBX) which will control the LEDs so as to indicate the activation of a function which may or may not have been initiated by the depression of an adjacent key.
Some telephones also have provision for the installation of optional devices such as extended keyboards 1012. Like the base telephone 112, the extended keyboard can include its own set of keys 1008 and LEDs 1010 whose functions are controlled by the PBX. Indicators across the base telephone unit and attached options (such as the extended keyboard 1012 of FIG. 10) typically operate to the user perception at various rates called cadences (usually a finite set). Cadences determine the nature of cycles of periods for indicators to be alternately on or off within a telephone. These cadences are used to indicate various states of the phone.
ROLMlink, a conventional digital telephony specification, defines 8 cadences (Cadence 0-Cadence 7). For example, a single cadence is used to indicate that an active phone call is associated with a line by having the indicator associated with the line key at a "solid" or always on cadence. As another example, a call waiting on another line would be indicated by the line key indicator at some specific periodic cadence.
The PBX (also referred to as the telephone switch) determines the cadence for individual indicators on each phone via commands or messages sent on the telephony link. A typical message from the PBX might cause an individual indicator to be set at a specific cadence, or all indicators to be set a specific cadence. The digital telephone and options keep track of the cadence each individual indicator is set to by the PBX and each has the responsibility to map these indicators to the periodic indication represented by the cadence corresponding to the indicator.
It is preferable for the user to have individual indicators operating at the same cadence across all units to be in synchronization (flash the same time as well as the associate rate). This gives the user a perception of a single system image, as opposed to a multiple system image. For example if one line on the base telephone 1002 and another line on the extended keyboard 1012 were both on "hold", the corresponding indicators would both be set (by the PBX) to the same periodic cadence. In order to make clearer to the user that both lines are, in fact, on "hold" (as opposed to in two different states) and to give the user a perception of a single system image, it would be preferable that they flash in synchronization.